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De Boni, Cristiano; Boehringer, Hans; Chon, Gayoung; Dolag, Klaus (2018): Evolution of the degree of substructures in simulated galaxy clusters. In: Monthly Notices of the Royal Astronomical Society, Vol. 478, No. 2: pp. 2086-2096
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We study the evolution of substructure in the mass distribution with mass, redshift, and radius in a sample of simulated galaxy clusters. The sample, containing 1226 objects, spans the mass range M-200 = 10(14) - 1.74 x 10(15)M circle dot h(-1) in six redshift bins from z = 0 to z = 1.179. We consider three different diagnostics: (1) subhaloes identified with SUBFIND;(2) overdense regions localized by dividing the cluster into octants;and (3) offset between the potential minimum and the centre of mass. The octant analysis is a new method that we introduce in this work. We find that none of the diagnostics indicate a correlation between the mass of the cluster and the fraction of substructures. On the other hand, all the diagnostics suggest an evolution of substructures with redshift. For SUBFIND haloes, the mass fraction is constant with redshift at R-vir, but shows a mild evolution at R-200 and R-500. Also, the fraction of clusters with at least a subhalo more massive than one thirtieth of the total mass is less than 20 per cent. Our new method based on the octants returns a mass fraction in substructures which has a strong evolution with redshift at all radii. The offsets also evolve strongly with redshift. We also find a strong correlation for individual clusters between the offset and the fraction of substructures identified with the octant analysis. Our work puts strong constraints on the amount of substructures we expect to find in galaxy clusters and on their evolution with redshift.